The present invention relates generally to an electric drill apparatus, and more particularly to an electric drill apparatus having a low profile and adapted to automatically re-drive a drill motor when rotation of the drill motor is stopped in the event of overloading.
Nowadays, in new construction, repair and the like of a variety of buildings and so on, there exists a need for drilling workpieces comprising structural materials such as a steel cage and the like at or near positions at which the workpieces are attached to buildings. It is therefore necessary to transport an electric drill apparatus to workpiece assembly places. In addition, a drilling operation must be often performed in a relatively narrow space at or near a position at which a structural material or workpiece is attached. Thus, to enable easy transportation and operation in narrow operating spaces, a reduction in size and weight is required for electric drill apparatuses.
A conventional electric drill apparatus typically comprises a slide mechanism which is automatically or manually movable in a vertical direction along a side surface of a body of the apparatus. The electric drill apparatus further comprises a motor, an annular cutter movable in the vertical direction by way of the slide mechanism, and a transmission mechanism for transmitting power of the motor to the annular cutter, which are arranged in the vertical direction or in the same direction as that of movement of the slide mechanism. Such vertically-arranged electric drill apparatuses are generally large in size, and can thus be only used in limited operation areas and have limited portability.
In contrast, WO 00/54915 describes an electric drill of a relatively low profile, in which a slide mechanism for sliding an annular cutter has a rotation axis which is substantially perpendicular to a rotation shaft of a drill motor. Such a low profile type electric drill apparatus is reduced in overall length as compared with the vertically-arranged type, and its compact size increases its portability.
In addition, Japanese Patent Publication (Kokoku) No. 3-78205 and Japanese Patent Public Disclosure (Kokai) No. 2003-25122 describe vertically arranged type electric drill apparatuses, each of which comprises a function of automatically stopping driving of a motor in the event of overloading.
However, such a low profile type electric drill apparatus as above, which is small in size and light in weight suffers from a drawback in that it has a limited drilling capability since only a small adhesive force acting on an electromagnetic base is employed to secure the electric drill apparatus on a workpiece.
Also, although the automatic electric drill apparatuses described in the above Japanese Official Gazettes have an automatic stop function when motor overload occurs, the function is provided to an electric drill apparatus comprising an automatic shift mechanism which moves an annular cutter in a vertical direction. There exists no electric drill apparatus having a manual shift mechanism for an annular cutter and a control means for automatically stopping driving of a motor when motor overload occurs. Further, there exists no electric drill apparatus having a function of re-driving a motor after it has been automatically stopped due to motor overload.